Direct Access Storage Devices (DASD) or disk drives have been assembled with two types of actuators; the stacked type actuator whereby each arm and its associated structure are stacked onto a spindle and shaft with appropriate spacers disposed between adjacent actuator arms in order to provide spacing of the arms for engagement with associated disk surfaces, and the comb type actuator where the actuator is either machined or molded with the actuator comb being single piece with a plurality of members extending therefrom to act as attachment points for the actuator load beams. The comb type is more difficult to manufacture because of the complexity of assembling the load beams, sliders and associated wiring to a fixed structure of the comb. Two types of actuator supports exist; a live or rotational shaft to which the actuator arms and spacers of a stacked actuator are fixed, and a dead or fixed shaft upon which a hub rotates, through a bearing set. The hub of the dead shaft stacked actuator carries the actuator arms and spacers. Some live shaft actuators have hubs also which carry the actuator arms and shafts.
The prior art DASDs have had flanged hubs which are placed with the flanges accurately positioned relative each other and/or relative to a known datum plane. The hubs are axially parallel and spindle shafts support the hubs and the flanges. The flanges, one for the stacked actuator and one for the stacked disk pack, comprise locating surfaces upon which the actuator assembly and the disk pack are assembled.
The prior art of which U.S. patents U.S. Pat. No. 5,189,577 issued to Nishida et al., U.S. Pat. No. 5,227,936 issued to Strickler et al. and U.S. Pat. No. 5,291,357 issued to Uda are exemplary, forms stacked actuators and stacked disk packs by placing actuator arms and spacers over the actuator hub and by placing the disks and the spacers over the disk hub, where the locating surfaces or locating flanges of the respecting spindles are disposed such that they are between the actuator arms or the disks and the base or frame of the disk drive. FIG. 1 is a schematic representation of a live shaft actuator disk drive having actuator arms and spacers disposed between the locating flange and the base or datum plane. FIG. 2 is a schematic representation of the stacked type disk drive assembly found in Nishida et al, Strickler et al, or Uda.
As is well known in the industry, each arm, spacer or disk is designed with a nominal height or thickness dimension and a stated or specified tolerance. One of skill in the art will appreciate that as the spacers and the actuator arms or disks are stacked on their respective hubs, cumulative tolerance buildup occurs. As the buildup of the tolerances occurs, the clearance between the actuator arm and the adjacent disk surface must be designed to be sufficient to accommodate any worst case tolerance buildup condition in order to prevent the actuator arm from rubbing against the disk surface which thereby would damage the disk surface and render the disk ineffective for recording of digital data.
As disk drives are reduced in size to fit into laptop and notebook sized computers, the vertical dimension of the disk drive assembly continues to be very tightly constrained by standards such as the PCMCIA standard. As the vertical dimension is so tightly constrained, any addition of a few thousandths of an inch to each actuator arm/disk clearance which are not required consumes scarce and valuable height. Furthermore, designs such as illustrated in FIG. 1. become impractical because the live shaft design of that type DASD require the jaw shaped shaft support necessary to support both ends of the rotatable live shaft 114. The portion 138 above the moveable actuator, having a bearing mounted therein, cannot be accommodated in a low profile DASD such as a PCMCIA standard DASD due to the height constraints imposed by the PCMCIA standards.
While tolerances may be defined more tightly to alleviate some of these clearance problems, wherever possible, the cost of manufacture greatly increases with such tightening of the tolerances to the point that the dimensional gain is offset by the manufacturing cost increase and therefore becomes impractical.